Bone fixation system

ABSTRACT

An implant for fixation of a bone includes a shaft having a proximal end and a distal end, and a longitudinal axis defined between the proximal end and the distal end. A plurality of blades are disposed on the shaft, and are helically twisted about the longitudinal axis. At least one of the blades has a variable blade width that increases in a direction along the longitudinal axis. A mechanism for coupling the implant to a second fracture fixation implant may be provided separately or in combination.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. application Ser. No.09/978,002, filed Oct. 17, 2001 now U.S. Pat. No. 6,835,197.

FIELD OF THE INVENTION

The present invention relates generally to a system for fixation of twoor more parts of a fractured bone. More specifically, the presentinvention relates to a bone implant and locking apparatus for internalfixation of a long bone, such as a femur.

BACKGROUND OF THE INVENTION

Fractures commonly occur in the femur, and especially in the femoralneck and intertrochanteric regions. Traditionally, these fractures havebeen treated using a nail located in the femoral head in cooperationwith a side plate located on the outside of the femur, or in cooperationwith an intramedullary nail located in the intramedullary canal. Thenail cooperates with the side plate or intramedullary nail to align andcompress the bone fragments.

A high incidence of death is associated with hip fractures due to theinjury itself or related complications. Frequent complications may arisewhen two or more bone fragments are forced towards each other when thepatient supports his or her weight on the healing bone. For example, asharp implanted nail or hip screw may cut through and penetrate thefemoral head or neck; or a nail, hip screw, side plate, orintramedullary nail may bend or break under load where the contactbetween bone fragments is insufficient for the bone itself to carry thepatient's weight.

A variety of compressible fixation systems have been developed tomaximize bone to bone contact while permitting bone fragments to migratetowards one another. For example, helical blades have been developedthat may be inserted into and secured to the neck of a femur, andcoupling mechanisms have been developed to slidably couple the helicalblade to a side plate or intramedullary nail.

The prior art blades, however, may be susceptible to migration withinthe bone fragment and, even worse, may break free or pull out of thebone fragments, thus allowing the bone fragments to separate and/orbecome misaligned. Prior art blades are also susceptible to bendingstresses, which may lead to undesirable bending or breakage of theblade.

In addition, many prior art coupling mechanisms provide unlimitedamounts of sliding between the blade and the side plate orintramedullary nail, which may lead to disassembly of the blade and sideplate/intramedullary nail. Furthermore, prior art coupling mechanism areoften complicated and difficult to assemble during implantation.

Thus, a need exists for improved bone fixation systems.

SUMMARY OF THE INVENTION

The present invention is directed to bone fixation system includingimplants and coupling mechanisms for fixation of a bone. According toone aspect of the invention, an implant for fixation of a bone includesa shaft having proximal and distal ends and defines a longitudinal axisbetween the proximal and distal ends. A plurality of blades, each havingproximal and distal ends, are disposed on the shaft and are helicallytwisted about the longitudinal axis. According to one embodiment, theplurality of blades may twist about 90° around the longitudinal axis. Atleast one of the blades may have a variable blade width that variesalong the longitudinal axis. For example, the variable blade width mayincrease in a direction from the blade proximal end toward the bladedistal end. Additionally or alternatively, at least one of the bladesmay have a variable blade height that varies along the longitudinalaxis. For example, the variable blade height may increase in a directionfrom the blade proximal end toward the blade distal end. The variableblade height is preferably substantially zero at the blade proximal end,such that the proximal end of the blade is substantially flush with theproximal end of the shaft.

According to a further aspect of the invention, the shaft of the implantmay define a bladed portion and a non-bladed portion. The non-bladedportion may define a non-bladed diameter, and the bladed portion maydefine a bladed diameter that is smaller than the non-bladed diameter.In addition, the non-bladed portion may include a tapered region locatedsubstantially adjacent the bladed portion, wherein the tapered regiondefines a tapered region diameter that decreases in a direction towardthe bladed portion. The tapered region may further define a neckdiameter at a point substantially adjacent the blades that is smallerthan the blade diameter.

The present invention is also directed to a coupling mechanism forcoupling a first fracture fixation implant to a second fracture fixationimplant. The coupling mechanism includes a body member receivable in thefirst implant and including a single prong extending from the body forcontacting a surface of the second implant. The coupling mechanismfurther includes a drive member rotatably coupled to the body member forthreadable engagement with the first implant. The drive member rotatesfreely with respect to the body member and may be used to urge the bodymember toward the second implant such that the single prong contacts thesurface of the second implant and substantially prevents rotation of thesecond implant with respect to the first implant. More specifically, thesingle prong may define a first engagement surface, the second implantmay define a second engagement surface, and the first and secondengagement surfaces may interact to substantially prevent rotation ofthe second implant with respect to the first implant.

According to a further aspect of the invention, the single prong maylimit sliding of the second implant with respect to the first implant.For example, the second engagement surface may include stops formedadjacent at least one of its ends for contacting the prong to preventfurther sliding of the second implant.

The coupling mechanism may also be provided in a system for fixation ofa fractured bone, which includes first and second fracture fixationimplants.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description will be better understood in conjunction withthe accompanying drawings, wherein like reference characters representlike elements, as follows:

FIG. 1 is a perspective view of one illustrative embodiment of afracture fixation system according to the present invention, shownimplanted in a femur;

FIG. 2 is a left side view of an illustrative embodiment of a fracturefixation implant of FIG. 1;

FIG. 3 is a top view of the implant of FIG. 2, with portions shown incross-section;

FIG. 4A is a front view of the implant of FIG. 2;

FIGS. 4B to 4F are cross-sectional views of the implant of FIG. 2, takenalong lines B—B to F—F of FIG. 2, respectively;

FIG. 5 is a right side view of an illustrative embodiment of a couplingmechanism according to the present invention, shown inside the secondfracture fixation implant of FIG. 1;

FIG. 6 is a right side view of the second implant of FIG. 5;

FIG. 7 is an enlarged, cross-sectional view of a portion of the secondimplant of FIG. 5;

FIG. 8 is a front view of a body member of the coupling mechanism ofFIG. 5;

FIG. 9 is a left side view of the body member of FIG. 8, with portionsshown in cross-section;

FIG. 10 is a right side view of the body member of FIG. 8;

FIG. 11 is a top view of the body member of FIG. 8;

FIG. 12A is a partial cross-sectional view of the coupling mechanism ofFIG. 5;

FIG. 12B is a partial cross-sectional view of an alternative embodimentof the coupling mechanism of FIG. 5, including a two-pronged bodymember;

FIG. 13 is a perspective view of a drive member of the couplingmechanism of FIG. 5;

FIG. 14 is a cross-sectional view of the drive member of FIG. 13;

FIG. 15 is right side view of an end cap of the second implant of FIG.6;

FIG. 16 is a back view of the end cap of FIG. 15;

FIG. 17 is a perspective view of an illustrative embodiment of aninsertion handle for use with an implant system according to the presentinvention; and

FIG. 18 is a perspective view of the insertion handle of FIG. 17, showncoupled to the second implant of FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a fracture fixation implant 20 according to oneembodiment of the present invention is shown implanted in a femur andcoupled to a second fracture fixation implant 22, which is shown forillustrative purposes as an intramedullary nail 22. Implant 20 may beused in conjunction with an intramedullary nail 22 or other fracturefixation member to treat orthopaedic trauma, impending bone fractures,and bone fractures. For example, implant 20 may be used to treatintertrochanteric fractures of the femur. Implant 20 is not limited touse in conjunction with an intramedullary nail 22, however, and may beused alone or in conjunction with any number of implants, bone plates,etc., known to one of ordinary skill in the art. Furthermore, thepresent invention is not limited to treatment of the femur, and may beused to treat any of the bones in the human and/or animal bodies.

Referring to FIGS. 2 and 3, implant 20 includes a shaft 24 having aproximal end 26 and a distal end 28, and defines a longitudinal axis 30between the proximal and distal ends 26, 28. A plurality of blades 32are disposed on shaft 24 and are helically twisted about longitudinalaxis 30, as will be discussed in more detail below. The plurality ofblades 32 has a proximal end 34 and a distal end 36, and blade proximalend 34 is preferably located substantially adjacent shaft proximal end26. Blades 32 may alternatively be located on shaft 24 at anintermediate position between shaft proximal and distal ends 26, 28.

A cannulation 38 (shown in FIG. 3) may optionally be provided in shaft24 and oriented substantially coaxially with longitudinal axis 30. Ifprovided, cannulation 38 may be sized to permit insertion of a guidewire (not shown) to aid in the alignment of implant 20 during theimplantation procedure, as is commonly known in the art. Shaft distalend 28 may be configured and dimensioned for attachment to an insertiondevice (not shown), such as an insertion handle or driving cap. Forexample, as shown in FIGS. 2 and 3, shaft distal end 28 may be angledwith respect to shaft longitudinal axis 30 and/or include a recess 35having a threaded portion 37 for attachment to an insertion device. Asbest seen in FIG. 1, recess 35 may have a non-symmetrical shape, such asa D-shape, so that the rotational orientation of implant 20 can bereadily ascertained from distal end 28.

Referring to FIGS. 4A–4F, implant 20 is preferably provided with fourhelical blades 32 a–2 d that twist about longitudinal axis 30. One ofordinary skill in the art will know and appreciate, however, thatimplant 20 may be provided with any number of blades 32, such as five,six, or eight blades. Blades 32 a–32 d each have a helical twist aboutlongitudinal axis 30, which is shown as approximately 90°. Thus, eachblade is rotated approximately 90° about longitudinal axis betweenproximal end 34 (shown in FIG. 4A) and distal end 36 (shown in FIG. 4F).The helical twist is such that once implant 20 is driven into a bone,e.g., the femur, the helical twist of blades 32 substantially preventsimplant 20 from sliding in the bone along longitudinal axis 30. One ofordinary skill in the art will know and appreciate that blades 32 mayhave any amount of helical twist about longitudinal axis 30, such as,for example, 45°, 60°, 120°, 180°, 360°, 720°, or 1080°.

As shown in FIGS. 4A–4F, a first blade 32 a and a second blade 32 c aresubstantially diametrically opposed from one another about longitudinalaxis 30, and a third blade 32 b and a fourth blade 32 d are alsosubstantially diametrically opposed from one another about longitudinalaxis 30. First and second blades 32 a, 32 c are preferably about 90° outof phase with respect to third and fourth blades 32 b, 32 d, howeverother configurations are within the present invention. Preferably in oneembodiment, at least one of the blades 32 defines a blade width W thatvaries along longitudinal axis 30. More specifically, blade 32 b has ablade width Wb that increases from blade proximal end 34 (shown in FIG.4A) to blade distal end 36 (shown in FIG. 4F), such that blade width Wbis greatest substantially adjacent blade distal end 36 and smallestsubstantially adjacent blade proximal end 34. Preferably, blade width Wbgradually tapers outward from proximal end 34 to distal end 36.

In the illustrative embodiment shown, blades 32 b and 32 d both havevariable blade widths Wb and Wd, respectively. When implant 20 is in theintended rotational orientation within the bone, shown in FIG. 1, thedistal ends 36 of blades 32 b and 32 d are substantially aligned withthe plane in which the majority of forces are applied to implant 20 (asubstantially vertical plane, in the view of FIG. 1, extending throughlongitudinal axis 30 and longitudinal axis 68). Thus, the greater widthsWb, Wd of blades 32 b, 32 d around distal ends 36 increase the bendingstrength of implant 20, while the decreased widths at proximal ends 34provides for ease of insertion of implant 20 into the bone. The taper ofblades 32 b and 32 d also helps to prevent sliding of implant 20 withinthe bone along longitudinal axis 30.

Additionally or alternatively, one or more of the blades 32 may have asubstantially constant blade width W. For example, as shown in FIGS.4A–F, blade 32 c may have a substantially constant width Wc that issubstantially equal at blade proximal end 34 (shown in FIG. 4A), at theintermediate points shown in FIGS. 4B–4E, and at blade distal end 36(shown in FIG. 4F). In the illustrative embodiment shown, blade 32 aalso has a substantially constant blade width Wa (blade width Wa appearsto vary in FIGS. 4A–4F due to the variance in blade height Ha, discussedbelow, however blade width Wa is actually substantially constant alonglongitudinal axis 30).

According to a further aspect of the present invention, at least one ofthe blades 32 may define a blade height H (defined perpendicularly tolongitudinal axis 30 from the base of the blade 32 to the tip of theblade) that varies along longitudinal axis 30. In particular, blade 32 amay have a blade height Ha that increases from blade proximal end 34(shown in FIG. 4A) to blade distal end 36 (shown in FIG. 4F), such thatblade height Ha is greatest substantially adjacent blade distal end 36and smallest substantially adjacent blade proximal end 34. Preferably,blade height Ha is substantially zero at blade proximal end 34, as shownin FIG. 4A, such that blade 32 a is substantially flush with shaft 24 atproximal end 34. When implant 20 is in the intended rotationalorientation of FIG. 1, the decreased height Ha or substantially flushconfiguration of blade 32 a at proximal end 34 increases the distance Ximplant 20 must migrate in the bone before it cuts completely throughthe bone. Also, the flush configuration of blade 32 a at proximal end 34reduces migration of implant 20 in the bone (because there is virtuallyno blade 32 a at proximal end 34 to cut through the bone when a load isapplied).

Additionally or alternatively, at least one of the blades 32 may have asubstantially constant blade height H. For example, as shown in FIGS.4A–4F, blades 32 b, 32 c, and 32 d each have substantially constantblade heights Hb, Hc, and Hd, respectively, that are substantiallyconstant from blade proximal end 34 (shown in FIG. 4A) through theintermediate points shown in FIGS. 4B–4E, and at blade distal end 36(shown in FIG. 4F).

Referring back to FIG. 3, implant 20 includes a bladed portion 40, uponwhich blades 32 are disposed, and a non-bladed portion 42 that iswithout any blades 32. Bladed portion 40 defines a bladed diameter 44and non-bladed portion 42 defines a non-bladed diameter 46. The maximumdiameter of bladed portion 40 (i.e., where bladed diameter 44 is at itsgreatest) may preferably be smaller than the maximum diameter ofnon-bladed portion 42 (i.e., where non-bladed diameter 46 is at itsgreatest). According to this configuration of implant 20, bladed portion40 may pass freely through bore 66 in intramedullary nail 22 (shown inFIG. 5 and discussed in detail below) to provide ease of assembly, andnon-bladed portion 42 may mate with bore 66 to provide a stable slidinginterconnection between non-bladed portion 42 and bore 66.

Non-bladed portion 42 may be further provided with a tapered region 48located substantially adjacent the bladed portion 40. Tapered region 48defines a tapered region diameter 50 that decreases in a directiontoward bladed portion 40. For example, tapered region diameter 50 may,at the location adjacent to the untapered region, be equal to non-bladeddiameter 46 and decrease, or taper inward, along longitudinal axis 30towards the distal end of bladed portion 40. Preferably, tapered region48 is curved inwardly to provide even stress distribution throughout thetapered region 48, and to provide a uniform bending of implant 20 underloading. Additionally or alternatively, tapered region 50 may furtherdefine a neck diameter 52 at a point substantially adjacent bladedportion 40 (at the point where non-bladed portion 42 meets bladedportion 40) that is smaller than bladed diameter 44. This configurationof implant 20 provides for bone ingrowth between the non-bladed portion42 and the bladed portion 40, thereby providing resistance againstimplant 20 from backing out of the bone. In addition, tapered region 48serves to self-center implant 20 as implant 20 is inserted into bore 66of intramedullary nail 22 (shown in FIG. 5).

The present invention is also directed to a mechanism which may be usedto couple a first fracture fixation implant 20 to a second fracturefixation implant 22. As described herein, the coupling mechanism may beused to couple implant 20, described above, to an intramedullary nail22. The coupling mechanism, however, is not limited to use with implant20 and/or intramedullary nail 22, and may be used to couple any numberof different fracture fixation implants known to those of ordinary skillin the art.

Referring to FIG. 5, a body member 60 and a drive member 62 are shownassembled into an interior channel 64 in intramedullary nail 22. Bodymember 60 and drive member 62 cooperate with channel 64 to secureimplant 20 (not shown) in a bore 66 that extends through intramedullarynail 22. As will be discussed in more detail below, body member 60,drive member 62 and channel 64 cooperate to substantially preventimplant 20 from rotating about its longitudinal axis 30 (shown in FIGS.1–3) within bore 66, and also to limit sliding of implant 20 within bore66 to a predetermined distance.

Referring to FIGS. 6 and 7, the configuration of intramedullary nail 22is shown in detail. Intramedullary nail 22 defines a longitudinal axis68 that may be straight, bent (shown), curved, or otherwise configuredand dimensioned to mate with the geometry of the bone into whichintramedullary nail 22 is to be implanted. Channel 64 extendssubstantially along longitudinal axis 68, and is dimensioned andconfigured to receive body member 60 and drive member 62, such that thetwo parts may move in channel 64 at least partially along longitudinalaxis 68. A series of threads 98 may be disposed on channel 64, as willbe discussed in detail below. Also, a pair of grooves 65 may be formedon channel 64, and are preferably diametrically opposed from oneanother.

Still referring to FIGS. 6 and 7, bore 66 extends through intramedullarynail 22 and intersects with channel 64, and is dimensioned andconfigured to allow implant 20 to slide therethrough. According to theillustrative embodiment shown, bore 66 is configured and dimensioned toslidably engage non-bladed portion 42 of implant 20, and maintainimplant 20 in angular relationship with respect to longitudinal axis 68.As shown, bore 66 is disposed at an angle 70 with respect tolongitudinal axis 68. Angle 70 may be selected to match the anatomy ofthe patient in which intramedullary nail 22 and implant 20 are to beimplanted, for example, to correspond to the femoral neck/shaft angle ofa human patient. A cannulation 72 (partially shown in FIG. 7) mayoptionally be provided through intramedullary nail 22 in substantialcoaxial alignment with longitudinal axis 68. If provided, cannulation 72may be sized to permit insertion of a guide wire (not shown) to guidethe implantation of intramedullary nail 22 into the bone, as is commonlyknown in the art.

Referring to FIGS. 8–11, body member 60 is shown in detail. Body member60 includes a substantially cylindrical portion 78 that defines alongitudinal axis 80 of the body member 60, and a prong 76 extendingfrom cylindrical portion 78. One of ordinary skill in the art will knowand appreciate, however, that body member 60 is not limited to the shapeshown, and may have any shape that permits body member 60 to move withinchannel 64 of intramedullary nail 22. A pair of alignment tabs 85 (shownin FIGS. 8 and 11) may extend from cylindrical portion 78. If provided,tabs 85 are positioned on body member 60 such that tabs 85 may bereceived in grooves 65 (shown in FIG. 7) of intramedullary nail 22.Cooperation between tabs 85 and grooves 65 substantially limits rotationof body member 60 within channel 64 of intramedullary nail 22.

Cooperation between tabs 85 and grooves 65 also maintains surface 79(illustrated in FIG. 9) of body member 60 at a distance from implant 20when the coupling mechanism is assembled and locked, thus allowingimplant 20 to freely slide in bore 66. More specifically, grooves 65have ends 67 (shown in FIG. 7) that contact tabs 85 and prevent bodymember 60 from sliding any further towards bore 66. Ends 67 are locatedin channel 64 at locations such that tabs 85 contact ends 67 (to preventfurther movement of body member 60 towards bore 66) before surface 79contacts implant 20. As shown in the figures, surface 79 is preferablyoriented at an angle 81 with respect to longitudinal axis 80 that issubstantially equal to angle 70, although angle 81 may be different thanangle 70. According to the configuration where angle 81 is substantiallyequal to angle 70, angled surface 79 remains at a constant distance fromimplant 20 when the coupling mechanism is assembled and locked.

Body member 60 may also include an attachment portion 82, which isconfigured and dimensioned to rotatably couple body member 60 to drivemember 62, as will be discussed in more detail below. As shown in FIG.8, attachment portion 82 includes a pair of upward-extending arms 83that define a pair of opposed channels 83 a for receiving a portion ofdrive member 62 therein. A cannulation 84 may optionally be providedthrough body member 60 in substantial coaxial alignment withlongitudinal axis 80 to permit insertion of a guide wire (not shown)therethrough.

Still referring to FIGS. 8–11, prong 76 extends away from body member 60in a direction substantially parallel to longitudinal axis 80, and maybe configured and dimensioned to contact implant 20 to limit sliding androtation of implant 20 with respect to longitudinal axis 30 (shown inFIG. 1). As will be discussed in more detail below, prong 76 may beprovided with a first engagement surface 86 that contacts a secondengagement surface 90 formed on implant 20 to substantially preventrotation of implant 20 and limit sliding of implant 20, as will bediscussed in more detail below. According to alternative embodiments ofthe present invention, body member 60 may be provided with two or moreprongs to contact two or more engagement surfaces formed on implant 20.For example, a second prong may extend from body member 60 in the samedirection as prong 76, and may be diametrically opposed to prong 76about longitudinal axis 80 and substantially parallel to prong 76. Thetwo-pronged embodiment may be used, for example, with an implant 20having two diametrically opposed engagement surfaces. Alternatively, asingle-pronged embodiment may be used with an implant 20 having two ormore engagement surfaces.

Referring back to FIGS. 2 and 3, an exemplary embodiment of secondengagement surface 90 is shown formed on implant 20. According to theembodiment shown, second engagement surface 90 is substantially flat andextends along longitudinal axis 30. First and second stops 92, 94 may belocated at opposite ends of locking second engagement surface 90. In theillustrative embodiment shown, second engagement surface 90 is recessedinto shaft 24 of implant 20, and stops 92, 94 are formed at theboundaries of the recessed surface. One of ordinary skill in the artwill know and appreciate, however, that other configurations ofengagement surface 90 and stops 92, 94, are within the presentinvention. For example, engagement surface 90 and/or stops 92, 94 mayalternatively be formed on or extend from shaft 24. Furthermore, asdiscussed above, implant 20 may alternatively be provided with two ormore second engagement surfaces 90, which may interact with a bodymember 60 having one, two or more prongs.

When implant 20 is received in bore 66 in intramedullary nail 22 andbody member 60 is located in channel 64 with tabs 85 bottomed out onends 67 of groves 65, prong 76 interacts with implant 20 tosubstantially prevent rotation of implant 20 about its longitudinal axis30. More specifically, prong 76 fits tightly in the space betweenchannel 64 and implant 20 such that first and second engagement surfaces86, 90 are maintained in contact under the constraints of channel 64. Inthis configuration, implant 20 is substantially prevented from rotationabout its longitudinal axis 30 due to abutment of substantially flatfirst and second engagement surfaces 86, 90. The coupling mechanism maythus be used to maintain implant 20 in its intended rotationalorientation within the bone. If provided, stops 92, 94 prevent implant20 and implant 22 from coming apart, and may also limit the amount ofsliding of implant 20 along its longitudinal axis 30 to the length ofsecond engagement surface 90. For example, once implant 20 slidesdistally until first stop 92 contacts prong 76, any further sliding inthe distal direction is prevented. Likewise, once implant 20 slidesproximally until second stop 94 contacts prong 76, any further slidingin the proximal direction is prevented. Thus, first and second stops 92,94 may be selectively spaced apart along longitudinal axis 30 to providefor a desirable amount of sliding between implant 20 and intramedullarynail 22, such as to provide for compression between the two fracturedbone fragments. For example, limited sliding may be desirable duringimplantation, to compress a fractured femur head toward the trochantericregion. Additionally, limited motion may also stimulate bone growth andfracture healing during service. One of ordinary skill in the art willknow and appreciate that first engagement surface 86 and secondengagement surface 90 are not limited to the substantially flatconfigurations shown herein. Rather, first and second engagementsurfaces 86, 90 may have any geometries that, when located adjacent oneanother, prevent rotation of implant 20 about axis 30, yet provide forsliding of implant 20 along longitudinal axis 30.

As discussed above, body member 60 may have two or more prongs 76, andimplant 20 may have two or more engagement surfaces 90. While multipleprongs may be desirable in certain applications (such as whereextraordinarily large forces tend to rotate first implant 20 about itslongitudinal axis 30 with respect to second implant 22), the exemplaryembodiment having a single prong 76, shown in FIGS. 8–10, oralternatively having one prong longer than the other, provides forincreased ease of assembly over the two-pronged or multi-prongedembodiments having equal length prongs. For example, a single prong 76,or one prong longer than the other, may be advantageous in the instanceshown in FIG. 12A, where implant 20 is misaligned in bore 66 such thatfirst engagement surface 86 is misaligned with second engagement surface90. In this instance, movement of body member 60 toward implant 20causes prong 76 to slide along second engagement surface 90 to influenceimplant 20 to rotate about longitudinal axis 30 until first and secondengagement surfaces 86, 90 are flush with one another, and moreover, areengaged to substantially prevent rotation of implant 20. To thecontrary, when a two-pronged embodiment having equal length prongs, asshown in FIG. 12B, is moved toward an implant 20 that is misaligned inbore 66, one of the prongs 76 contacts shaft 24 and prevents the otherprong 76 from contacting the respective second engagement surface 90 torotate implant 20 into alignment. As shown, second prong 76 b is incontact with shaft 24 and prevents first prong 76 a from contactingsecond engagement surface 90 a to rotate implant 20 into properalignment with body member 60. Thus, a single-pronged embodiment (or amulti-pronged embodiment having one prong longer than the other) mayprovide for increased ease of assembly of the coupling mechanism.

Referring back to FIGS. 7, 8 and 11, tabs 85, if provided, cooperatewith grooves 65 to substantially prevent body member 60 from rotatingwithin channel 64 of intramedullary nail 22. This provides the advantageof aligning prong(s) 76 with engagement surface(s) 90 in channel 64;thus, implant 20 can easily be inserted into bore 66 without requiringthe surgeon to address the alignment of prong(s) 76.

Referring to FIGS. 13 and 14, drive member 62 is shown in detail. Drivemember 62 is configured and dimensioned to engage channel 64 toselectively hold body series of threads 96 which mate with a series ofthreads 98 formed in channel 64, however other structures for securingdrive member 62 in channel 64, such as springs or elastomers, are alsowithin the present invention. Drive member 62 also includes anattachment portion 100 which is configured and dimensioned to rotatablycouple drive member 62 to body member 60, such that drive member 62 mayfreely rotate with respect to body member 60. This is especially usefulin the case where tabs 85 (FIGS. 8 and 11) cooperate with grooves 65(FIG. 7) to prevent rotation of body member 60 in channel 64. In theexemplary embodiment shown, attachment portion 100 is a substantiallydisc-shaped flange that may be received between the channels 83 a formedin arms 83 of body member 60. One of ordinary skill in the art will knowand appreciate that any number of structures may alternatively beprovided to couple drive member 62 to body member 60 and provide forrotation between the two parts, such as, for example, screws, swivels,pins, etc. One of ordinary skill in the art will also know andappreciate that body member 60 and drive member 62 may be eitherpermanently attached, or detachably coupled to one another. Drive member62 may also include a tool-engaging portion 102. As shown, drive member62 defines a substantially hex-shaped opening 102 that is dimensionedand configured to engage a hex key. Tool-engaging portion 102 mayalternatively be dimensioned and configured to engage any number ofdriving tools known to one of ordinary skill in the art, such as a screwdriver or wrench. A cannulation 104 may optionally extend substantiallyaxially through drive member 62 to permit insertion of a guide wire (notshown) therethrough.

Referring to FIGS. 15 and 16, an optional end cap 106 is shown. End cap106, if provided, may be removably attached to the end of intramedullarynail 22 to conceal body member 60 and drive member 62 in channel 64. Inaddition, in the case where the surgeon chooses not to engage thelocking mechanism (e.g., does not tighten drive member 62 in channel 64in order to engage body member 60 with implant 20), end cap 106 may beurged against drive member 62 to prevent drive member 62, andconsequently body member 60, from unintentionally migrating withinchannel 64.

In the illustrative embodiment shown in FIGS. 15 and 16, end cap 106includes a series of threads 108 disposed thereon, which mate with theseries of threads 98 formed on channel 64, or another series of threadsformed on channel 64, to secure end cap 106 on intramedullary nail 22.Any number of structures known to one of ordinary skill in the art,including snap fasteners, adhesives or screws may alternatively be usedto removably attach end cap 106 to intramedullary nail 22. End cap 106may further include a tool-engaging portion 110, shown as asubstantially hex-shaped portion 110 that is dimensioned and configuredto engage a wrench. Tool-engaging portion 110 may alternatively bedimensioned and configured to engage any number of driving tools knownto one of ordinary skill in the art, such as a hex-key or screw driver.A cannulation 112 may optionally be provided, which extendssubstantially axially through end cap 106 to permit insertion of a guidewire (not shown) therethrough.

Intramedullary nail 22 may be provided with body member 60, drive member62 and, optionally, end cap 106 preassembled into channel 64, thusreducing the amount of time associated with implanting intramedullarynail 22, as well as reducing the amount of parts that must be handled bythe surgeon. In the case where these components are preassembled,cannulations 72, 84, 104, and 112 (provided in intramedullary nail 22,body member 60, drive member 62, and cap 106, respectively) may besubstantially aligned to permit insertion of a guide wire (not shown)completely through the preassembled unit. Thus, a guide wire may be usedto guide intramedullary nail 22, including the preassembled lockingcomponents, into the intramedullary canal of a fractured bone.

As shown in FIGS. 17 and 18, an insertion handle 120 may optionally beprovided to aid with insertion of the second implant (e.g.,intramedullary nail 22). As shown, insertion handle 120 includes ahandle portion 122 and a coupling portion 124. Coupling portion 124 mayinclude a bore 125 that is dimensioned and configured to receive acoupling screw 126. Coupling screw 126 may be inserted through bore 125and threaded into threads 98 of channel 64, to detachably coupleinsertion handle 120 to intramedullary nail 22. One of ordinary skill inthe art will know and appreciate, however, that other structures may beemployed to detachably couple insertion handle 120 to intramedullarynail 22. When attached to intramedullary nail 22, insertion handle 120may be used to aid insertion of intramedullary nail 22 into theintramedullary canal. A cannulation 128 may optionally be provided incoupling screw 126 and aligned with cannulations 72, 84, and 104(discussed above), to permit use of insertion handle 120 to insertintramedullary nail 22 over a guide wire. Furthermore, the length L ofcoupling screw 126, shown in FIG. 17, may be selected such thatinsertion handle 120 may be coupled to intramedullary nail 22 with bodymember 60 and drive member 62 preassembled therein.

While preferred embodiments and features of the bone implant andcoupling mechanism have been disclosed herein, it will be appreciatedthat numerous modifications and embodiments may be devised by thoseskilled in the art. It is intended that the appended claims cover allsuch modifications and embodiments as fall within the true spirit andscope of such claims and that the claims not be limited to or by suchpreferred embodiments or features.

1. An implant for fixation of a bone comprising: a shaft having aproximal end and a distal end, the shaft defining a longitudinal axisbetween the proximal end and the distal end; and a plurality of bladesdisposed on at least a portion of the shaft and helically twisted aboutthe longitudinal axis, the plurality of blades having a proximal end anda distal end; wherein at least one of the blades has a variable bladewidth that varies in a direction along the longitudinal axis, and atleast one of the blades has a variable blade height that varies in adirection along the longitudinal axis, such that a cross-section takenin a plane substantially perpendicular to the longitudinal axis of theimplant between the proximal and distal ends of the plurality of bladesdefines both the variable blade width and variable blade height at apoint along the implant.
 2. The implant of claim 1, wherein the variableblade width increases in a direction from the blade proximal end towardthe blade distal end.
 3. The implant of claim 1, wherein the variableblade height is greatest at the blade distal end.
 4. The implant ofclaim 3, wherein the variable blade height increases in a direction fromthe blade proximal end toward the blade distal end.
 5. The implant ofclaim 3, wherein at least one of the blades has a substantially constantblade height.
 6. The implant of claim 4, wherein the variable bladeheight is substantially zero at the blade proximal end.
 7. The implantof claim 4, wherein: at least one of the first and second blades has asubstantially constant blade height; and at least one of the third andfourth blades has a substantially constant blade width.
 8. The implantof claim 7, wherein: the first and second blades have a variable bladewidth that increases in a direction along the longitudinal axis, and asubstantially constant blade height; the third blade has a blade heightthat increases in a direction along the longitudinal axis, and asubstantially constant blade width; and the fourth blade has asubstantially constant blade height, and a substantially constant bladewidth.
 9. The implant of claim 8, wherein the first and second bladesare out of phase with the third and fourth blades by about 90° about thelongitudinal axis.
 10. The implant of claim 1, wherein at least one ofthe blades has a substantially constant blade width.
 11. The implant ofclaim 1, wherein the plurality of blades twist about 90° about thelongitudinal axis.
 12. The implant of claim 1, wherein the plurality ofblades comprises: at least first and second blades substantiallydiametrically opposed from one another about the longitudinal axis; andat least third and fourth blades substantially diametrically opposedfrom one another about the longitudinal axis; wherein at least one ofthe first and second blades has a variable blade width that increases ina direction along the longitudinal axis, and at least one of the thirdand fourth blades has a variable blade height that increases in adirection along the longitudinal axis.
 13. The implant of claim 1,wherein the implant is configured and dimensioned for implantation in afemoral head.
 14. The implant of claim 1, further comprising acannulation extending from the proximal end to the distal end, thecannulation configured and dimensioned to receive a guide wire.
 15. Theimplant of claim 1, wherein the distal end is configured and dimensionedfor attachment to an insertion device.
 16. An implant for fixation of abone comprising: a shaft defining a longitudinal axis of the implant,the shaft including a bladed portion and a non-bladed portion; and aplurality of blades disposed on the bladed portion of the shaft andhelically twisted about the longitudinal axis, the plurality of bladeshaving a proximal end and a distal end; wherein the non-bladed portionincludes a tapered region located substantially adjacent the bladedportion, wherein the tapered region defines a tapered region diameterthat decreases in a direction toward the bladed portion.
 17. The implantof claim 16, wherein at least one of the blades has a variable bladeheight that increases in a direction from the blade proximal end towardthe blade distal end.
 18. The implant of claim 17, wherein the variableblade height is substantially zero at the blade proximal end.
 19. Theimplant of claim 16, wherein at least one of the blades has asubstantially constant blade height.
 20. The implant of claim 16,wherein at least one of the blades has a variable blade width thatvaries in a direction along the longitudinal axis.
 21. The implant ofclaim 20, wherein the variable blade width increases in a direction fromthe blade proximal end toward the blade distal end.
 22. The implant ofclaim 16, wherein at least one of the blades has a substantiallyconstant blade width.
 23. The implant of claim 16, wherein the pluralityof blades twist about 90° about the longitudinal axis.
 24. The implantof claim 16, wherein the implant is configured and dimensioned forimplantation in a femoral head.
 25. The implant of claim 16, furthercomprising a cannulation extending from the proximal end to the distalend, the cannulation configured and dimensioned to receive a guide wire.26. The implant of claim 16, wherein the bladed portion and thenon-bladed portion each have an outer diameter and the maximum outerdiameter of the bladed portion is smaller than the maximum outerdiameter of the non-bladed portion.
 27. The implant of claim 16, whereinthe tapered region is configured and dimensioned to provide even stressdistribution over the tapered region.
 28. The implant of claim 16,wherein the tapered region is concave.
 29. The implant of claim 16,wherein the tapered region provides uniform bending of the implant. 30.The implant of claim 16, wherein the tapered region further defines aneck diameter at a point substantially adjacent the blades, wherein theneck diameter is smaller than the blade outer diameter.
 31. The implantof claim 16, wherein the implant has proximal and distal ends located onthe longitudinal axis, and the bladed portion is located substantiallyadjacent one of the ends.
 32. The implant of claim 31, wherein thedistal end of the implant is configured and dimensioned for attachmentto an insertion device.